function [imr,img,imb,imf]=RGB2BGR(filename)    % 函数RGB2GBR
    im=imread('atk.png');                       % 图片名字
    imr=im(:,:,1);
    img=im(:,:,2);
    imb=im(:,:,3);
    imf=cat(3,imb,img,imr);
    for i=1:4
    figure
    switch i
    case 1
    img=imf(end: -1:1, :); % 使图像垂直翻转
    imshow(img);
    case 2
    imb=imf(:, end: -1:1); % 使图像水平翻转
    imshow(imb);
    case 3
    imr=imf(1:2:end,1:2:end,:); % 使图像尺寸减半
    imshow(imr);
    case 4
    % 使图像中心区域100*100变红
    % [m,n,~]=size(imf);
    % imf(m/2-50:m/2+50,n/2-50:n/2+50,1)=255;
    % imf(m/2-50:m/2+50,n/2-50:n/2+50,2)=0;
    % imf(m/2-50:m/2+50,n/2-50:n/2+50,3)=0;
    imshow(imf,'border','tight','initialmagnification','fit');
    set (gcf,'Position',[20,20,680,408]);
    axis normal;
    saveas(gca,'logo-alientek.png','png');
    end
    end